"Only recently have we begun to understand that we need a critical mass (usually considered one third of the members of any group) for women and other 'outsiders' to be seen as unexceptional."

This week on Ask a Woman, we’re examining the question of why Yahoo CEO Marissa Mayer has gotten so much press attention—and discussing how difficult it is for women in high-level jobs to have so little company at the top.

Why do you think that there is so much press attention given to Marissa Mayer’s ascension to CEO of Yahoo? It is clear that she is an extremely talented individual who has the ability and drive to push Yahoo forward in its next chapter. I really don’t recall this level of attention during the announcement of the prior CEO.

Two words: numbers matter.

Even the extremely talented Marissa Mayer is not immune from the press scrutiny that all outsiders receive when so few of us occupy positions of power. Only 20 women head Fortune 500 companies; Mayer is the 20th. The scrutiny is even more intense because she got the job without having been a CEO previously, which is highly unusual, and because she announced her pregnancy. As a result, we hear constantly about her intention to return to work within a short time of delivering—and we also hear complaints that she’s setting a “bad example” for other mothers.

When we watch an able woman like Marissa Mayer being subjected to this level of scrutiny, we are again reminded of how much attention the press pays to gender—not just when a woman gets a high-level job, but forever after. How often have our last three U.S. secretaries of state (Madeleine Albright, Condoleezza Rice, and Hillary Rodham Clinton) read comments in the news about their appearances rather than their policies? Americans aren’t alone here: Christine Lagarde, head of the International Monetary Fund, and German Chancellor Angela Merkel also receive far too much gendered attention.

One of our earliest studies at The White House Project examined how the U.S. press tends to cover political races involving just one woman. We dubbed it our “hair, hemlines and husband” study. If there is only one woman in a race, press coverage focuses heavily on her hair, her clothes, her love life—any topic closely associated with her gender. The presence of two women in a single race invites either direct physical comparisons or “catfight” references. It’s only when three women are competing in a single race—which is still a rarity—that each woman is assessed as a candidate first.

We need to look more closely at the number of women who hold top jobs in the first place as a determining factor in how women in power are viewed and treated. Only recently have we begun to understand that we need a critical mass (usually considered one third of the members of any group) for women and other “outsiders” to be seen as unexceptional. A trailblazing Catalyst study defined “three” as the turning point for the “normalization” of women on boards.

The good news is that the intense press scrutiny of Marissa Mayer provides an opportunity to remind Americans that women still don’t lead alongside men in comparable numbers, even though most people assume we do. Only 4% of Fortune 500 CEOs are women, and Marissa Mayer is one of them. That is a long way from fair.